将套接字从Python select的读取列表传递到另一个函数

Question

I am using Python's select library to asynchronously read data off of two sockets. Since the size of the packets that I receive can vary, and I don't know if there is a maximum possible size for the data that I am reading, I have implemented a function called recvAll(sock) to get all of the data off of a socket:

def recvAll(sock):
    buffer = ''
    data = []

    try:
        while True:
            buffer = sock.recv(8192)
            if not buffer:
                break
            data.append(buffer)
    except error, (errorCode, message):
        if errorCode != 10035:
            print 'error: ', str(errorCode), ' ', message
    return "".join(data)

I am calling the select library like this:

rlist, wlist, elist = select.select([sock1, sock2], [], [])
for sock in rlist:
    if sock == sock1:
        #data1 = sock.recv(8192)
        data1 = recvAll(sock)
    else:
        #data2 = sock.recv(8192)
        data2 = recvAll(sock)

In the for loop for each socket I process, if I call sock.recv directly, I am able to properly get data1 and data2. However, if I first pass sock to recvAll I am only able to get data1. It does not appear that recvAll is being called on sock2 at all. Why is this the case?

Answer 1

Most likely what is going on is that, since your socket is not set as non-blocking ( socket.setblocking(0) ), your recvAll function is blocking, waiting for more input from the socket. It won't return 0 until the socket is closed by the other end, or an error occurs.

The way to fix this is to structure your code to combine the functions of recvAll with your select . Each time your select returns with an indication that there is data waiting on the socket, read from the socket ONLY ONCE, append the data to the buffer for that socket, then loop back into select .

After each recv , look at what you got and decide what to do next.. eg. for some protocols, if the buffer contains a \\n , that would be an indication that you got a complete message and need to do something with it. Or, in your case, it seems that closing of the socket is the indication that your message is complete.. so you should look for recv returning a zero length string....

If the socket was in fact closed, then you need to remove it from the list of sockets you are passing into select .